1. Field of the Invention
The present invention relates to an optical pickup which makes it possible for information recorded in an optical recording medium to be read out and information to be recorded on an optical recording medium by irradiating light on the optical recording medium. In particular, the present invention relates to structure to prevent collision between an objective lens which is provided with the optical pickup and the optical recording medium.
2. Description of Related Art
Optical recording media such as a compact disc (hereinafter referred to as a CD) and a digital versatile disc (hereinafter referred to as a DVD) are widely available. In addition, researches on an optical recording medium which can be performed recording of information in high density are being carried on in recent years in order to further increase recording capacity of the optical recording medium. For example, a high density optical recording medium such as an HD-DVD or a Blu Ray Disc (hereinafter referred to as a BD) has been available in the market.
For a case to reproduce information from such optical recording medium or for a case to record information on the optical recording medium, an optical pickup which includes a light source, an objective lens that makes light emitted from the light source focus on a recording layer of the optical recording medium, and a photo receiving element that receives reflection light reflected by the recording layer, is used.
In the optical pickup it is necessary to control a focusing position of the objective lens such that focus of light which is emitted from the light source is always matched on the recording surface of the optical recording medium irrespective of waving of surface of the optical recording medium or the like when reading out or recording of information is performed. For this purpose, structure is employed in that control is performed such that a position of the objective lens which is held by a lens holder is moved by an optical lens actuator in order to make distance between the objective lens and the optical recording medium always constant. In below described explanation, there may be a case where such control is referred to as a focus servo.
By the way, when information recorded on an optical recording medium that can be performed the above described high density recording, for example, a BD, is read out by the optical pickup, for example, it is necessary that spot size of light spot which is formed on the optical recording medium is made small. As for method to make spot size of the light spot small, it is usually performed to make wavelength of light which is emitted from the light source shorter and at the same time to make numerical aperture of the objective lens larger.
However, if the numerical aperture of the objective lens is made larger, space between tip of the objective lens and the optical recording medium (working distance; WD) becomes narrower when the optical pickup is operated. Tendency for this WD to become narrower is remarkable especially in the optical pickup which can be applied to the BD, for example. As the WD becomes narrower as above described, possibility of occurrence of the collision between the objective lens and the optical recording medium is made much higher, for example, when the optical recording medium in that waving of its surface is large, is used or when the focus servo becomes out of control, or the like due to scratch that is made on surface of the optical recording medium, vibration from outside, or the like.
It should be noted that the situation where the WD becomes narrower is not limited only to the optical pickup which can be applied to the BD, and there may be a case where it happens in the optical pickup which is applied to the optical recording medium such as a CD or a DVD, for example. That is, as for a note type personal computer or the like, because it is requested that it is made thinner, the objective lens which is provided in the optical pickup, has a small diameter lens. In such case, too, the WD becomes narrower. Therefore, in such case, too, possibility of occurrence of the collision between the objective lens and the optical recording medium becomes very high.
Because of these reasons, in order to avoid that information recorded on the optical recording medium may become non-readable, or the optical pickup may become non usable because of damage to the objective lens, by the collision between the objective lens and the optical recording medium, various structures are proposed conventionally in which a protector for prevention of the collision is provided. It should be noted that, as for the protector for prevention of the collision, it is required that the protector is hard to damage the optical recording medium and hard to be worn out in itself when the collision with the optical recording medium happens. It is because to prevent deterioration of reproduced signal caused by alteration of state of the optical recording medium.
As for structure of the protector for prevention of the collision that has been conventionally proposed, there is structure in which a protector that is composed by a molded article is provided on a lens holder to hold the objective lens. For example, see JP-A-2006-120246, or JP-A-2001-209956. As for another structure of the protector for prevention of the collision, there is structure in which a coating layer is provided on outer layer of a protecting portion to prevent the collision between the objective lens and the optical recording medium. For example, see JP-A-2003-242703, JP-A-2006-338783, or JP-A-2002-222535. It should be noted that, in this case, examples are shown in which the protector for prevention of the collision is attached on a lens holder, and in which the protector for prevention of the collision is attached on the objective lens.
However, in case of the structure in which the protector composed by the molded article is provided on the lens holder, it causes a problem that it cannot sufficiently restrain damage on the optical recording medium or stain by abrasion of the protector by only using merely the molded article such as polyacetal or the like that is plastic softer than the optical disc.
In this regard, in JP-A-2006-120246, it is intended to solve the above described problem by means that utilizing the molded article composed of silicon rubber composite in which compounding agent that contains at least one of polyurethane particle and fluorine contained resin powder is mixed, as the protector. However, in case of the structure disclosed in JP-A-2006-120246, it causes problem in cost because it is the structure in that the molded article is formed utilizing a specially compounded composition.
Further, as the structure for the protector which is provided on the lens holder, in case where a portion that has a curved surface is formed as disclosed in JP-A-2001-209956, it causes a problem that a load for working operation increases when the optical pickup is manufactured because dimensional control for it is not easy.
Further, in case where structure is employed in which the coating layer that has special composition is provided on the protector portion as disclosed in JP-A-2003-242703, JP-A-2006-338783, or JP-A-2002-222535, though it has a merit that it is good at tolerance at height, it causes a problem that cost for it increases.